Treatment of alkaline bauxite residue

Abstract

A process is disclosed for treating a Bayer process waste comprising a slurry containing bauxite residue and dissolved aluminium. The process comprises supplying the waste to a settling area to cause the bauxite residue to settle out of the slurry, thereby producing a supernatant liquor. The process further comprises neutralizing the supernatant liquor with a solution containing magnesium and calcium to produce a neutralized slurry containing precipitated hydrotalcites and thickening the neutralized slurry to produce a clarified effluent and a compacted slurry containing the precipitated hydrotalcites, part of said compacted slurry being recirculated to the supernatant liquor to be neutralized and / or directly to the neutralizing step The clarified effluent and the compacted slurry are disposed of separately. Also disclosed is a plant for treating a Bayer process waste.

Description

TECHNICAL FIELD[0001]The invention disclosed relates to the production of alumina from bauxite. In particular, it relates to waste produced by the Bayer process in the course of extracting alumina from bauxite. More particularly, a process is disclosed for treating a Bayer process waste comprising bauxite residue and dissolved alumina.BACKGROUND ART[0002]Subjecting bauxite to the Bayer process produces a pregnant caustic liquor containing dissolved alumina and a bauxite residue slurry. In order to extract alumina from the pregnant liquor, it is first subjected to solid liquid separation steps to separate the bauxite residue. The alumina-bearing liquor is then treated to precipitate aluminium trihydroxide that is subsequently refined to produce alumina, which is in turn processed into aluminium metal.[0003]The separated bauxite residue is often in the form of a slurry that contains a significant volume of caustic liquor. The slurry is delivered to storage ponds where the bauxite resi...

AI Technical Summary

Benefits of technology

The patent describes a process for treating liquid waste from plants that use the Bayer process for making chemicals. The process involves using a flocculant to settle the waste liquor and prepare it for further treatment. This process can be used to dispose of waste from such plants, rather than simply storing it in large ponds. The process can also be used on an industrial scale and can process the entire output of a plant. The recycling of compacted slurry containing hydrotalcite can improve settling and capture contaminants from the waste liquor. Adding a flocculant to the process can also improve settling behavior and allow for higher treatment rates of the waste. The process reduces fresh water consumption and minimizes damage to the flocculant during transfer. Additionally, using excess seawater can act as a buffer against poor quality effluent. The process can involve dewatering or mixing the compacted slurry directly with residue from the refinery. Overall, the patent describes a technical solution for efficiently processing and disposing of waste from chemical plants.

Problems solved by technology

This means that the liquid portion of waste from a Bayer process can be treated to remove heavy metals and other materials that make the untreated liquid portion unsuitable for disposal.

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